Fastener Finish K Factors

Documents

Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.

Quotation

• The fastener family (Fastener Finish K Factors) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
• Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
• Quantity per size and your target delivery date.
• Destination country, and any required documents (for example a mill test certificate) so the quote includes them.

Sample & supply

Minimum order quantity is 10,000 pieces. Stock items run 3–7 days. Quantities or variants outside the standard range are confirmed at quotation.

Storage & shipping

Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.

How do I use a K factor to get from wrench torque to bolt preload?

The working relation is T = K × F × d, with T the wrench torque, F the bolt preload, d the nominal diameter and K the nut factor from this table. It is deliberately a lumped model: K folds thread friction, bearing friction and geometry into one number so the arithmetic stays simple at the bench. The catch the table makes visible is that K is a property of the whole surfaced system — bolt finish, nut finish, washer, lubricant, speed — not of the bolt alone. A zinc-flake bolt at K 0.11 torqued with a K 0.20 assumption lands roughly 45% under the intended preload; the same error against a rusty surface at 0.39 overtorques toward yield. So: pick K from the row matching what is actually on the parts as installed (including wax topcoats and thread-break-in compound), verify by measuring bolt elongation or using a tension-indicating method on critical joints, and treat the tabulated values as starting points to be validated on your joint per DIN 946-style testing — the source's own determination note is the model for that.

Why is the rusty-steel K factor (0.39) so much higher than everything else, and what does that mean for reused hardware?

Because corrosion products and surface roughness drive friction up, and higher thread and bearing friction means more of the wrench torque is spent overcoming friction instead of stretching the bolt — at K 0.39 against an assumed 0.18, the same torque delivers barely half the intended preload, which is how corroded joints end up loose despite correct-looking torque marks. For reused fasteners the table is a caution in both directions: the rusty row warns what weathered hardware does to preload, while the lubricant rows warn that brushing oil onto an old bolt changes its K downward and can overload it at the original torque setting. The sound practice for any joint where the preload matters is to restore a known surface condition — clean, specified finish or specified lubricant — and re-derive the torque from the matching K row, or replace the hardware. Where reuse is unavoidable, quote the condition on the RFQ and the finish system is supplied to restore a defined K.